Polishing machines for grinding and polishing the ends of fiber optic cables are usually of the type having a rotating abrasive disk that is maintained relatively flat. The optical fiber is secured in a fixture having a flat bottom. The end of the optical fiber that is to be polished projects slightly below this bottom surface, sometimes under the urging of a spring mechanism to control the forces on the fragile optical fiber. The fixture, with its fiber optic cable attached, is carefully lowered onto the rotating abrasive disk and made to undergo a standard polishing pattern such as circular or figure eight. There are usually three or more stages of polishing that must be done in sequence, from relatively course abrasive to very fine. In the final stage the bottom surface of certain fixtures contacts the abrasive disk so that the end of the optical fiber is polished to a flat surface that is normal to the longitudinal axis of the connector terminated to the fiber optic cable. However, this subjects the bottom surface of the fixture to wear and it must be replaced occasionally. Other prior art fixtures rely upon the tips of the optical fibers themselves in contact with the abrasive surface to maintain the axes of the fixture and the cables somewhat perpendicular to the surface of the abrasive material. In these fixtures the fixture itself does not contact the abrasive material and therefor does not wear, however, the perpendicularity of the final polished surface to the axis of the cable is dependant upon variations in the manufacturing of the terminated cables. That is, when the cables are loaded into the fixture they are positioned with respect to some feature of the connector such as a shoulder. This results in the tips of the optical fibers extending below the bottom surface of the fixture by varying amounts, the three tips that extend the farthest being the ones that establish the initial angle between the axes and the abrasive surface. With such an arrangement some of the optical fibers are over polished while others may be under polished resulting in inconsistency and varying quality. Fixtures used with these machines are frequently complex, especially those utilizing spring mechanisms such as is disclosed in U.S. Pat. No. 4,330,965 which issued May 25, 1982 to Clark. Simpler fixtures are in use such as those disclosed in U.S. Pat. Nos. 4,819,386, which issued Apr. 11, 1989 to Struyf and 4,276,926 which issued Jun. 16, 1981 to Tamulevich. The '386 patent discloses a fixture having a body with a number of cavities or nests, each for receiving a terminated fiber optic cable, and a retainer plate that is assembled to the body after the cables are in place to hold them captive. The connector attached to the end of the cable has a spring element that is compressed within the nest thereby urging the optical fiber toward and past the bottom of the fixture. This spring element that is part of the connector, provides a similar benefit as the spring element in the more complex fixture disclosed in the '965 patent mentioned above. However, this fixture is dependent on the terminated cable having a spring biased connector.
In all of the above prior art fixtures the terminated end of the cable is located in the fixture by banking a feature of the connector or cable on a shoulder or some other surface of the fixture and allowing the tips of the cables to extend past the bottom surface of the fixture by random amounts. In the case of a single cable fixture this presents no problem, however, in multiple cable fixtures problems of alignment and quality arise.
What is needed is a relatively simple fixture that locates the tips of the optical fibers in a plane that is parallel with the abrasive surface prior to polishing and where the fixture is maintained in this plane during polishing, thereby obviating the alignment and quality problems mentioned above or the need to contact the abrasive material to maintain vertical alignment. Additionally, such a fixture should not need to be taken apart to receive the fiber optic cables for polishing, assembled, and then again taken apart to remove the finished cables.